@online{HOL4web,
  author={HOL4 devs},
  title={{The HOL4 Interactive Theorem Prover}},
  url={https://hol-theorem-prover.org},
  year={2020},
  date={2020-07-29}}

@online{polymlweb,
  author={PolyML devs},
  title={{The PolyML implementation of Standard ML}},
  url={https://www.polyml.org/index.html},
  year={2020},
  date={2020-08-04}}